1. Field of the Invention
The present invention relates to a protection circuit of a hard disk drive, and more particularly, to a head protection circuit that protects a write head and a magneto-resistive (MR) read head by bypassing electrostatic charge applied to the write head when the power of a preamplifier is turned “off.”
2. Description of the Related Art
A hard disk drive includes a plurality of heads magnetically paired to rotating magnetic disks. The heads read or write information by magnetizing or sensing a magnetic field of the rotating disks.
The heads are integrated on slider/head units (or a head-gimbal assembly (HGA)), and the slider/head units are typically attached to an actuator arm mounted on a base plate of the hard disk drive in a likely way to rotate through a suspension or a head arm. The actuator arm includes a voice coil coupled to a magnetic assembly (or a yoke) mounted on the base plate. The voice coil forms a voice coil motor together with the magnetic assembly. The voice coil motor rotates the actuator arm to move the heads on the disks. The disks, actuator arm, and voice coil motor are usually assembled within a sealed housing called a hard disk drive assembly (HDA).
Generally, a magnetoresistive (MR) head for reading and an inductive write head installed near the magnetoresistive head for writing are installed on the slider/head units. For convenience, the term MR read-write head is used to denote the MR read head and the write head together or to denote the integration of them.
In the write operation of the hard disk drive, voltages with different waveforms are applied to the ends of the write head. Accordingly, common mode voltage and differential mode voltage exit on the ends of the write head. Due to these voltages, electrostatic charge exists at the ends of the write head, and currents flow to the write head due to the electrostatic charge even after the write operation is finished. Thus, not only is the write head overheated but also the MR read head is affected by a so-called write-to-read (WR) cross-talk, i.e., an interference between signal lines for a pair of differential write signals and signal lines for a pair of differential read signals. Consequently, the MR read head becomes more sensitive to electrostatic discharge (ESD).
On the other hand in the hard disk drive, it is known that electrostatic charge generated between the slider/head unit and the preamplifier, i.e., the head arm (or the suspension), is transmitted to the write head and the MR read head via the signal lines for the pair of write differential signals and the pair of differential read signals, respectively, or the electrostatic charge of the write head are transmitted to the MR read head. The write head can endure relatively high voltage and current because it includes an inductive coil, but the MR read head is especially sensitive to an overload of voltage and current because it is very small. Therefore, when the electrostatic charge is discharged via the MR read head, the MR read head may be damaged.